The present invention relates to a new and improved construction of an infrared radiation-burglary detector -- also referred to in the art as an infrared intrusion detector -- which is of the type comprising an optical system for focusing the radiation upon a radiation receiver.
Such detectors are constructed to receive infrared radiation emanating from a supervised room or area and upon variation of such infrared radiation to deliver an alarm signal by means of a suitable evaluation circuit. To detect an intruder or other person who has unlawfully entered the room or area which is supervised, there is preferably utilized infrared radiation within a wavelength range which is characteristic of the inherent radiation of humans, for instance the range up to 20 .mu. or particularly the range between 14 .mu. and 7 .mu.. However, instead of such there also can be employed external radiation from a radiation source in a suitable wavelength range which can be better handled, for instance in near infrared above 1 .mu., which is reflected by the individuals who are to be detected. In any event the permeability or the reflection capability of the optical system and the sensitivity of the radiation receiver must be tuned to this wavelength range.
In order to be able to already detect even the slightest movements of a person, for instance a burglar or other intruder, in the protected room or area, it has been found to be advantageous to provide individual separate receiving directions having intermediately situated dark zones or fields. During movement of the intruder and upon passing through one or a number of receiving regions, the radiation receiver thus is impinged in a pulse-like manner or with varying radiation intensity and the evaluation of such output signal for the purpose of delivering a signal can be accomplished in a simple manner by means of a conventional pulse detector or alternating-current voltage detector.
To produce such different mutually separated receiving regions it has become known in the art to provide a number of optical systems, for instance a number of lenses or spherical segment- or paraboloid reflectors, at the common focal point of which there is arranged the radiation receiver. In this way there can be provided a number of receiving regions corresponding to the number of optical systems. But such an arrangement is extremely complicated, especially when there are employed a large number of receiving directions, and further, the adjustment and readjustment is extremely cumbersome. Such type burglary or intrusion detectors therefore are not only complicated and expensive, but furthermore only can be accommodated with extreme difficulty to the desired operating conditions and are not effective in all instances.
Likewise known to the art is the technique of producing a conical ring-shaped receiving region by means of cone-shaped reflectors or conical lenses or prisms of revolution in conjunction with only a single optical system. To produce a number of receiving regions there would also be, however, required in this case a multiplicity of reflectors, rendering the arrangement extremely complicated and expensive. Therefore, such installations in practice have been limited to a single cone-shaped receiving region.
With a further arrangement which has become part of the state-of-the-art employing strip-shaped receiving regions, it is indeed possible to improve upon the operational reliability and effectiveness of the system, but there is still required a complicated optical system which is assembled together, for instance composed of surfaces having two different main radii of curvature or utilizing cylindrical lenses.